During periods of heavy rainfall, discoloured water enters the Third Creek catchment from White Rock Quarry, because stormwater flows too quickly to allow the installed engineered structures to remove all the sediment from the surface water.

Sediment control is an important part of protecting our aquatic environment downstream of mining and quarrying operations.

Stormwater is rainwater plus anything the rain carries along with it. At White Rock Quarry, sediment is generated when rain falls on disturbed surfaces, such as internal unsealed roads or unvegetated areas. Rainwater falling on to the site collects fine particles as it flows downstream. This stormwater or ‘surface water runoff’ then runs into constructed ponds called sediment basins (also known as stormwater ponds). Sediment basins are designed to slow the water and allow the sediment to fall out of suspension within the basin. When stormwater flows too quickly or too large a volume exists, sediment basins cannot always remove all sediment from the stormwater.

High sediment levels in surface water can cause environmental impacts to waterways or creeks, and therefore the Department for Energy and Mining (DEM) and the Environment Protection Authority (EPA) regulate the permissible sediment levels in water leaving mines and quarries across South Australia.